Absolutely right, I totally agree. Random scaling issues that you can't either see or control is exactly the opposite of what we want to be providing.
Can you email me (adam at heroku dot com) some links to your past support tickets? I'd like to investigate.
Thanks for running your app with us. Naturally, I expect you to move elsewhere if we can't provide you the service you need. That's the beauty of contract-free SaaS and writing your app with open standards: we have to do a good job serving you, or you'll leave. I wouldn't want it any other way.